Our long-term goal is sustainable reduction of the incidence of Lyme borreliosis (LB). We propose to achieve this safely and inexpensively by targeting vaccines to the reservoir hosts of the agent Borrelia burgdorferi. Building upon our proof-of-concept studies and extending the work's scope to include further definition of the key reservoir species, we will develop live attenuated vaccines for oral delivery in the field and initiate controlled vaccine trials at field sites. The field studies will also inform implementation of a reservoir-targeted plague vaccine (Project 7.3). This is a multidisciplinary, multi-institution translational research project. Specific aim 1 is further development of a vaccine that uses the vaccinia virus backbone of the commercial rabies vaccine to express OspA of B. burgdorferi and to (a) administer this to a major reservoir, the white-footed mouse, Peromyscus leucopus, and (b) evaluate different methods of field delivery of the vaccine. These studies will be carried out in collaboration with industrial partners Merial for the vaccine construct and with Foodsource Lures Corp for the bait. The primary endpoint for will be the prevalence of B. burgdorferi in nymphs of Ixodes scapularis after they fed on infected P. leucopus as larvae. This will be assessed by quantitative PCR of host-seeking nymphs in the spring of the year after vaccination. In years 3-5 these studies will be extended to include second generation poxvirus-based constructs (Project 7.2) or, as an alternative, Salmonella-based oral vaccines (Project 7.4). Specific aim 2 is assessment of the effectiveness of the oral vaccines from Aim 1 in controlled field trials on an island site off New England. The vaccine will first be directly administered to captured P. leucopus and then in a second trial by distributed bait with vaccine. In subsequent years vaccine targeting of P. leucopus will continue and will be extended to other reservoir species, as indicated by Aim 3, and on a mainland site. Specific aim 3 is determination of which vertebrate species besides P. leucopus are major source of infection for larval ticks and, as such, would be additional targets for vaccination for effecting reduction in nymphal infection. For this, we will individual nymphal ticks for B. burgdorferi and for identity of the species that was the source of the blood meal for the larval stage of the tick. The source of residual blood proteins and/or mitochondria! DNA will be identified by mass spectrometry of peptide digests and/or by PCR.